Self-sorting organization of two heteroditopic monomers to supramolecular alternating copolymers

Article abstract of DOI:10.1021/ja8035465

Self-sorting organization of two AB-type heteroditopic monomers led to the formation of linear supramolecular alternating copolymers driven by host-guest noncovalent interactions based on the bis(p-phenylene)-34-crown-10/paraquat derivative and dibenzo-24

Full text of DOI:10.1021/ja8035465

Published on Web 08/05/2008
Self-Sorting Organization of Two Heteroditopic Monomers to Supramolecular
Alternating Copolymers
Feng Wang, Chenyou Han, Chunlin He, Qizhong Zhou, Jinqiang Zhang, Cong Wang, Ning Li, and
Feihe Huang*
Department of Chemistry, Zhejiang UniVersity, Hangzhou 310027, P. R. China
Received May 13, 2008; E-mail: fhuang@zju.edu.cn
Self-sorting,1 whereby molecules can find and self-assemble their
corresponding recognition units within a complex mixture with high
Scheme 1. Formation of Supramolecular Alternating Copolymers 3
from Self-Sorting Organization of Heteroditopic Monomers 1 and 2
affinity and fidelity, is commonplace and critical in biological
systems. For example, the self-sorting hydrogen bond recognition
between relatively few nucleic acid bases results in an enormous
amount of information stored in DNA, which further lead to its
replication and transcription. However, few examples were reported
to construct synthetic polymeric systems, analogues to the biopoly-
mers such as DNA and RNA, using the principle of self-sorting.1c
Alternating copolymers have unique properties different from those
of random copolymers, and some have been shown to be useful
and guest units. At low concentration (below 103 mM), protons,
materials.2 Supramolecular polymers (suprapolymers) can form
such as the pyridinium protons and benzyl protons H5, on the fast-
when repeating units in traditional polymers are connected via
exchanging units have two sets of well-defined signals standing
noncovalent interactions instead of covalent interactions.3,4 Al-
for the cyclic and linear species, respectively. This phenomenon is
though there is considerable interest in supramolecular alternating
quite different from reported supramolecular polymers assembled
(block) copolymers,4 to the best of our knowledge, supramolecular
by fast-exchange complexations,3h for which only one set of signals
alternating copolymers based on self-sorting organization of low-
was observed. This can attribute to the presence of slow exchanging
molecular-weight monomers have not been reported yet. Herein,
interactions exerting significant effects on the fast ones. As the
we demonstrate that when self-sorting organization is applied to
concentration increased, the signals of pyridinium protons H2 and
two AB-type heteroditopic monomers, linear supramolecular al-
H3 shifted upfield while those of benzyl protons H5 moved
ternating copolymers can be obtained driven by host-guest
downfield. At high concentration (232 to 650 mM), the signals for
the cyclic species are no longer observed and all signals become
interactions.
For the successful preparation of supramolecular alternating
broad, confirming the formation of high-molecular-weight aggregates.
copolymers from self-sorting organization of two heteroditopic
Moreover, values of the fraction p of complexed crown ether
moieties9 at different initial concentrations were obtained (Table
S1) from the chemical shift change ∆0 of the fully complexed
paraquat unit, which was estimated to be 0.113 ppm for benzyl
protons H5.7 Then maximum possible polymerization degrees at
monomers H1-G2 and H2-G1 (H1, G2, H2, and G1 represent
host or guest moieties on the two monomers) driven by host-guest
interactions, it is required that the complexations between H1 and
G1 and between H2 and G2 should be much stronger than the
complexations between H1 and G2 and between H2 and G1 and
have 1:1 stoichiometries. We designed and prepared heteroditopic
monomers 1 and 2, from which we want to get supramolecular
alternating copolymer 3 by self-sorting organization. It is well-
known that bis(p-phenylene)-34-crown-10 (BPP34C10) and dibenzo-
24-crown-8 (DB24C8) form 1:1 complexes with paraquat deriva-
tives and dibenzylammonium salts, respectively.5,6 Furthermore,
the self-sorting studies on model compounds 4-77 demonstrated
that the complexations between BPP34C10 and paraquat derivative
moieties and between DB24C8 and dibenzylammonium moieties
are much stronger than the complexations between BPP34C10 and
dibenzylammonium moieties and between DB24C8 and paraquat
moieties.7 Therefore, the self-sorting organization of monomers 1
and 2 should lead to alternating arrangement of the two monomers,
which further self-organize into linear supramolecular alternating
copolymers 3 (Scheme 1). Here the two linkers between host and
guest moieties on the two monomers were designed to have totally
more than 20 atoms in anticipation for a relatively low critical
suprapolymerization concentration (CPC).3a,8
Figure 1. Partial 1H NMR spectra (400 MHz, 1:1 CDCl3/CD3CN, 20 °C)
of (a) 2; equimolar mixtures of 1 and 2 at different crown unit concentra-
tions: (b) 2, (c) 8, (d) 20, (e) 40, (f) 60, (g) 103, (h) 232, (i) 464, and (j)
650 mM; and (k) 1.
The concentration-dependent 1H NMR spectra of equimolar
solutions of 1 and 2 are complicated (Figures 1 and S7) due to the
coexistence of the slow- and fast-exchange complexations of host
9
11254 J. AM. CHEM. SOC. 2008, 130, 11254–11255
10.1021/ja8035465 CCC: $40.75
2008 American Chemical Society

C O M M U N I C A T I O N S
formation of supramolecular alternating copolymers 3 in solution
as confirmed by 1H NMR, CV, DLS, viscosity measurements, and
SEM. The degree of polymerization was dependent on the initial
concentrations of two monomers. Morphology control of suprapoly-
mers is essential for their future applications,14 and the construction
of various architectures in the self-sorting manner will be reported
in our future publications.
Figure 2. (a) Cyclic voltammograms (chloroform/acetonitrile (1/1, v/v),
298 K, scan rate 100 mV/s) of equimolar mixtures of 1 and 2 at different
crown concentrations. (b) Specific viscosity of chloroform/acetonitrile (1/
1, v/v) solutions of equimolar mixtures of 1 and 2 versus the crown
concentration (298 K). (c) Scanning electron micrography of (gold-coated)
fibers drawn from a high concentration solution of 1 and 2.
Acknowledgment. This work was supported by the National
Natural Science Foundation of China (20604020 and 20774086).
Supporting Information Available: Experimnetal details, syntheses
of 1 and 2, self-sorting organization of model compounds (4-7), and
other materials. This material is available free of charge via the Internet
at http://pubs.acs.org.
different initial concentrations were calculated using the Carothers
equation (Table S1).10 As the concentration increases, the calculated
size of aggregrates increases to truly large values and supramo-
lecular alternating copolymers are formed. For example, at 650 mM,
p ) 98.2% and n ) 56.5, corresponding to a polymer with a molar
mass of 126.1 kDa.
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(Figure 2a). The electrochemistry reduction process shows two clear
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In summary, we demonstrated that self-sorting organization of
two AB-type heteroditopic monomers 1 and 2 could result in the
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